Leonardite Quality Improvement for Soil Amendment

Abstract

Improvement of leonardite quality was performed so that the material could be used as soil amendment. Although leonardite contains high humic substances, its pH level is very low. The study therefore aimed at increasing the pH value of leonardite from Mae Moh mine. Dolomite was mixed at the rate of 0, 5, 10 and 15% and the mixture was incubated at 60% of the maximum water holding capacity for 28 days. The values of pH and %humic acid were used as the indicators. The results indicated that leonardite plus 5% dolomites was the most suitable with the highest value of humic acid (51.69%) and suitable pH value (pH 6.14). For another experiment, leonardite was mixed with dolomite at the rates of 0 and 5% plus rock phosphate at the rates of 0, 5, 7.5 and 10%, and the mixture was incubated at 60% of maximum water holding capacity for 28 days. This experiment aimed at increasing both the pH and %total P₂O₅ value of leonardite by dolomite plus rock phosphate. The values of pH, %total P₂O₅ and %humic acid were used as the indicators for suitable rate of the mixture which would be suitable as soil amendment. The results showed that leonardite mixed with 5% dolomite plus 10% rock phosphate exhibited the highest pH (6.39), and %total P₂O₅ (0.97%) and a relatively high level of humic acid (42.37%),. Therefore, improved leonardite obtained from this experiment is appropriate to be used as soil amendment.